The present invention relates to a system including a combustion furnace for combusting a specimen into a gaseous sample for subsequent analysis.
In existing combustion-type analyzers such as Model No. CS-44, commercially available from Leco Corporation, the carbon and sulfur content of steel, for example, can be determined from a solid specimen which is positioned in an induction furnace and combusted to provide a gaseous sample. The gaseous sample is subsequently analyzed by an infrared detector to ascertain the carbon dioxide (CO.sub.2) and sulfur dioxide (SO.sub.2) concentrations which are then displayed as the carbon and sulfur content of the specimen. Certain aspects of such a system are disclosed in a pending U.S. patent application entitled COMBUSTION APPARATUS FOR ANALYTICAL INSTRUMENTS, Ser. No. 291,763, filed on Sept. 25, 1972, now U.S. Pat. No. 3,923,464, and assigned to the present assignee, the disclosure of which is incorporated herein by reference.
Such systems are open-ended in that a carrier gas is introduced into the combustion chamber of the induction furnace to oxidize the specimen and carry the specimen gas through an infrared cell and then exhaust it to the atmosphere. With such systems, therefore, the concentration of the specimen gas increases from near zero as combustion begins, to a peak period which diminishes rapidly as a function of time. The detecting and displaying devices thus are time dependent and must rapidly respond to the pulse of specimen gas to provide an accurate indication of the carbon and sulfur content of the specimen. To accomplish measurement, an integrator circuit is employed for integrating the electrical pulse developed by the infrared detector in response to the pulse of gas.
Such systems have proven effective although the detectors and circuits required to respond to the momentary pulse of specimen gas must, of necessity, have a relatively short time constant and, therefore, are subject to noise interference. Additionally, due to the open-ended flow of the gas through the system, in some cases incomplete combustion of the specimen into the constituent gases occurs. Also in such systems, the gas flow rate must be carefully regulated to maintain it constant such that electrical integration of the signal from the detector can be accurately undertaken and reproduced from sample to sample. In the CS-44 system, only CO.sub.2 is measured to ascertain the carbon content of the sample, thus requiring the use of an expensive and troublesome catalytic converter for converting CO to CO.sub.2.